Various technical portfolios are applied to reduce greenhouse gas for prevention of global warming, but recently a CCS (carbon capture and storage) technology for capturing and storing CO2 is coming to the fore as a controllable large-volume greenhouse gas processing technology. The capture technology applied to the power plant as a technology, whereby CO2 is transported to a reservoir and stored to be isolated after it is captured from a large-volume carbon dioxide discharge source, can be classified largely into after-combustion CO2 capture, before-combustion CO2 capture and oxygen combustion CO2 capture technologies. Of these, the before-combustion CO2 capture technology is a technology, in which various fossil fuels are partially oxidized to manufacture synthetic gas (H2+CO) as shown in FIG. 1 and subsequently it is converted to hydrogen and carbon dioxide through water gas transition reaction and then hydrogen or carbon dioxide is separated, so that carbon dioxide is captured before it is discharged as a flue gas. This technology is a technology for not only capturing carbon dioxide but also producing hydrogen, and is assessed as a core technology for moving to a future hydrogen economy society. Because, not petroleum, but coal, biomass and organic waste can be used as a raw material, it is a future development technology in preparation for petroleum depletion and high oil prices. Factorial technology for development of before-combustion capture technology can be divided largely into a refinement field for removing impurities after gasification, a water gas transition and reaction field for converting synthetic gas into hydrogen and carbon dioxide, and a H2/CO2 separation field for separating the generated hydrogen and CO2 from each other.
Thus, water-gas shift (WGS) is indispensable for before-combustion carbon dioxide capture (CCS) from coal gasification and hydrogen production. Such WGS reaction is an exothermic reaction as shown in Reaction Formula 1, and generally goes through double-stage reaction of high temperatures (400 to 450° C.) and low temperatures (200 to 250° C.).CO+H2OH2+CO2 reaction heat: −41.1 kJ/mol  (Reaction Formula 1)
The synthetic gases generated from coal gasification include high-temperature, high-pressure and high-concentration CO. For example, synthetic gases produced from Conoco-Philips E-Gas include 37 mol % of CO at 42 atm and 927° C. In the case of high-concentration CO like this, a double-stage WGS reactor is indispensable. But since the gas condition is high-temperature and high-pressure, a heat exchanger is necessary for every stage, and since the concentration of CO participating in the reaction is high, it is very difficult to maintain the temperature inside the reactor isothermal using a huge amount of reaction heat generated during reaction.
In addition, although WGS is a reaction not affected by pressure, vaporization of water, which is important in WGS, hardly occurs in the case of high pressure. Especially if the temperature of synthetic gas is lowered by heat exchange, it is all the more so. Therefore, in order to WGS-process the synthetic gases obtained through coal gasification, it is preferable to proceed with WGS reaction in a high-temperature section as far as possible. However, because of thermodynamic equilibrium of the WGS reaction, a disadvantage that the CO conversion rate is not so high occurs at high temperatures.
Furthermore, because the synthetic gases generated from coal gasification are different in composition from the synthetic gases obtained through a conventional SR reaction (a natural gas modification reaction), the reaction heat generated through WGS is very high since a large quantity of CO should be processed. Unless the reaction heat is removed effectively, hot spots generate on the catalyst layer in the reactor. Such temperature rise becomes a problem of not only a deactivation of catalyst but also the CO conversion rate decreasing due to thermodynamic equilibrium.